There are many kinds of multiphase electrical machines having rotating members which carry electrical components and include a cylindrical conductor. One example of such a rotating member is a brushless exciter. The major structural component of a brushless exciter is typically a rotating cylindrical conductor made from magnetic steel and known as a diode wheel. The basic function of a brushless exciter is to generate an alternating current and convert that current into a direct current used to produce the rotating field for an electrical generator. Rectification is accomplished through the use of multiple diode circuits which are rigidly mounted to the diode wheel. For a three-phase wye system a minimum of six diodes is required. Typically, however, many more are used to provide spare legs, to accommodate multiple pole designs, and to provide high current carrying capacity. Where high current capabilities are needed, many diodes are connected in parallel to reduce the current flow through each diode. To protect such diodes from degradation due to overcurrent application, and to protect the exciter's operation from the effects of a shorted diode, designs typically include fuses connected in series with the diodes about the periphery of the diode wheel.
In brushless exciter designs that include many diode-fuse combinations in parallel, the failure of a single diode should not have an adverse effect on the remaining diode-fuse combinations. Although each of the remaining parallel fuses will be required to carry an increased current load, this current is usually within the design capability of the fuse. In recognition of this fact, a number of systems have been proposed for detecting single diode failures which have not resulted in a shutdown of the generator. Such systems are illustrated in U.S. Pat. Nos. 4,635,045, and 4,952,915, assigned to the assignee of the present invention.
In practice, however, it has been observed that a single fuse failure in a brushless exciter design which utilizes phase paralleling rings has the potential to cause a cascade failure of the other diode fuses, resulting in a forced outage of the exciter (and the generator). Therefore, there is a need for a design which prevents overload of adjacent diode fuses resulting from failure of another diode fuse, thus preventing unnecessary cascade failures and generator shutdown.